A compass is conventionally used to determine a direction of travel or to determine the bearing of, for example, an object relative to a fixed or moving point. As such, a compass includes a marker, herein referred to as a heading marker, which will point in a direction of travel, for one application of the compass, and which is pointed towards an object for which a bearing is required, for the other application of the compass. A compass also includes means to determine the direction of the heading marker with respect to a predetermined fixed direction, usually north.
Known compasses, including the above features, of which the Applicant is aware, include magnetic compasses, fluxgate-type compasses, gyroscope-type compasses, and the like. All these compasses suffer from inherent inaccuracies in different situations which are well known and which are not explained in further detail herein.
Since the location of a global positioning system (GPS) satellite network in orbit around the earth it has become possible to determine the location of objects or persons on the earth by communication between the satellites and GPS receiver modules carried by objects or persons. When used in association with moving objects and by utilizing position information obtained at intervals, a direction of travel can be determined, the GPS satellite network thus being used for a compass-type application. It will be understood that the compass-type application can only apply in association with moving objects and that the above principles cannot assist to provide a bearing for a distant object or to provide compass information on a stationary craft, or the like. It can also only provide for a direction of travel and not the direction of heading of an object or craft, as the actual direction of motion of a craft may not coincide with the heading of the craft.
Furthermore, U.S. Pat. No. 4,881,080 (United States of America (Navy)) proposes the use of two spaced apart antennae or GPS receiver modules on a ship, or the like, thus providing for the positions of the modules to be determined, which in turn provide heading and compass information. Accurate results clearly can only be obtained if the modules are spaced sufficiently far apart, both modules use the same satellites to prevent a difference in dilution of precision and position fixes are not interrupted due to insufficient satellites being available. This compass arrangement is not practical for most applications of conventional compasses, e.g. on smaller craft or for hand held applications. Also, due to the accurate measurements required on installation, it cannot be readily transferred from craft to craft.
U.S. Pat. No. 5,146,321 (Motorola) provides an improved system to the above but requires the manipulation of an antenna for its operation and this required manipulation creates a major problem, particularly when the system is used on moving objects where a continuous compass reading is required. A further major drawback of this system is that any change of attitude of a craft or object on which the system is used (roll or pitch), will seriously affect the accuracy of a compass reading provided.